This application claims the priority of German Application Nos. 197 20 857.6, filed May 17, 1997 and 197 27 321.1, filed Jun. 27, 1997, the disclosures of which are expressly incorporated by reference herein.
The present invention relates to a cardan-type joint for torsion-proof connection of two shafts with one another such as the connection which is known, for example, from German Patent Document DE 43 04 274 C1.
When used in vehicles, cardan-type joints of this type are severely stressed not only mechanically, by torque peaks and by overtensioning joint movements, but also thermally as a result of thermal conduction and heat radiation of very hot parts situated in the vicinity of the joints as well as by a movement-caused heat build-up of the joint components themselves. In the case of plastic parts, the loadability of the materials used is reduced by heating of the components so that thermal stressing of the cardan-type joints is also relevant to their mechanical loadability.
Many known cardan-type joints, and particularly cardan shafts of light-weight constructions, have respective flanges on the ends of the two shafts connected by the joint, which flanges have three driving pins axially projecting in the direction of the cardan-type joint. In this case, six driving pins are arranged in a mutually staggered manner and are uniformly arranged on the circumference of a common graduated circle. The driving pins are connected with one another in a torsion-proof manner by a flexible hexagonal joint ring provided with sockets in its corner points. Between the sockets, the joint ring is itself axially elastically deformable so that the two flanges connected by the joint ring can carry out limited angular movements in any direction during rotation. This angular movement axially undulates the joint ring and twists the legs of the polygon so that, within the scope of the elasticity, bending stresses and torsional stresses corresponding to Hooke""s law occur and are superimposed on the torque-caused operational stresses. As a result of this superimpostion of stresses, the strength limit of the materials may be reached. Accordingly, because of the fatigue strength of the cardan-type joints, only limited bending angles can be permitted.
Three driving pins per flange, thus resulting in a total of six driving pins in the cardan-type joint, are not absolutely required. Using only two pins per flange, resulting in a total of four driving pins, is also conceivable. In this case, however, because of the distribution of the circumferential stress on the small number of driving pins, these driving pins are subjected to more stress than when a higher number of driving pins is used. The use of four or more pins per flange, resulting in a total of eight or more driving pins in the cardan-type joint, is also conceivable. In this case, with the rising number of driving pins, the required joint diameter becomes larger and/or the tolerable bending angle becomes smaller. Therefore, three or six driving pins are frequently used as a compromise between stress on the components, on the one hand, and joint size, on the other hand.
German Patent Document DE 41 40 311 A1 shows a hexagonal joint ring made of a fiber reinforced material in the form of a ring disk, in the case of which axial sockets are embedded in the reinforced corner areas. The linear areas between two adjacent corners are formed by a relatively thin web which extends in the plane of the ring disk and is made of several cohesive layers of hardened fiber reinforced material. This web is relatively wide in the radial direction. During bending of the cardan-type joint, these webs are not only bent but also twisted. Although, in the case of relatively low bending stresses, the thin webs can be elastically bent, because the shape of the webs deviates considerably from rotational symmetry, during twisting of the webs, high tensions occur mainly at their interior and exterior edges.
The initially mentioned German Patent Document DE 43 04 274 C1 shows a hexagonal joint ring in which the sockets arranged in the corner areas are connected, in pairs, to one another by oval driving loops which themselves are closed and wound on the outside around two adjacent sockets. Specifically, wide centrally located driving loops and a pair of driving loops situated on an edge side are alternately arranged in the joint ring. The wide driving loop is approximately three times as wide as its radial wall thickness. The two narrow driving loops together are approximately as wide as the driving loop situated in the center. The driving loops are radially swivellable on the sockets so that, as an individual component, the shape of the joint ring can be flexibly changed. For holding all parts of the joint ring together and for preventing the entry of dirt, the parts of the joint ring are embedded in a rubber-elastic mass of low hardness and are completely enclosed. Because the radial wall thickness is relatively small in relation to the axially measured width of the driving loops, the loops offer good prerequisites for absorbing circumferential tension when low excess tensions in the curvatures of the driving loops are present. During bending of this cardan-type joint, the driving loops are tilted and also twisted, in which case high excess tensions occur at different points of the driving loops. During tilting, there is a one-sided edge support of the loop curvature on the socket which results in a concentration of tension at this location. During twisting of the relatively wide driving loops, in a manner similar to that of the webs of the joint disk according to German Patent Document DE 41 40 311 A1, excessive tensions occur at the edges although at a lower level than in the disk according to this document. This type of joint ring, therefore, does not offer good prerequisites for good mobility of the cardan-type joint with a simultaneously high torque load.
It is an object of the invention to improve the cardan-type joint of the above-mentioned type such that, in the event of a high mechanical and thermal stress, relatively large bending angles can easily be permitted during rotation.
This object is achieved in cardan-type joints for torsion-proof connection of two shafts with one another in which the connection is axially and/or angularly movable within certain limits. The joint includes flanges arranged at ends of the two shafts connected by the joint. Three driving pins axially project in the direction of the cardan-type joint on each of the flanges to provide six mutually staggered driving pins uniformly arranged on a circumference of a common graduated circle. A flexible, regular polygon-type, joint ring connects the driving pins with one another in a torsion-proof manner and is provided with sockets at corner points. The joint ring is axially elastically deformable between the sockets and is formed in several parts by a collar of several closed oval driving loops forming individual chain links. Each of the loops winds around two adjacent sockets, and each of the loops can be radially swivelled on the sockets so that a shape of the joint ring can change in a flexible manner.
The oval driving loops are swivellably disposed in an axially slidable manner on the driving pins by pairs of mutually corresponding mutual contact surfaces. These surfaces have circular-arc-shaped contours in a meridian section and are disposed on the sockets and on the driving loops. Accordingly, the driving loops can be swivelled on the sockets while carrying out an axial sliding movement so that, at least on the basis of the axial stroke alone which the driving pins carry out with respect to one another, the driving loops are not elastically deformed and, therefore, to this extent are not subjected to an additional stress. If the sliding surfaces have spherical designs, then even twistings can be isolated from the driving loops.
Further features and advantages of the invention will become clear. In addition, the invention will be described in connection with certain embodiments which are illustrated in the drawings.